Vibration isolation systems are known. Thus for example, DE 698 17 750 T2 (Inventors Erik Loopstra, Peter Heiland) shows a vibration isolation system, which is designed for supporting a lithography device. Therein, the load to be supported, which typically comprises a table and components like production equipment placed thereon, is mounted on air bearings.
For improving the vibration isolation, so-called active vibration isolation systems provide sensors and actuators, by which a selective counteracting control is made possible. In doing so, actuators of the vibration isolation system are energized and act against vibrations, which may act on to the system from exterior or may be generated by the load to be supported.
Especially in the semiconductor industry, with increasing miniaturisation of the components, the requirements for such vibration isolation systems are steadily increasing.
It is particularly a matter of low-frequency adjusted (<1 Hz) vibration isolation systems to be used in the lithography, with steppers, immersion systems and the like, particularly also such which have a very low horizontal stiffness.
According to methods known from practical experience for designing vibration isolation systems, the features of the system are characterized independently from external conditions by measuring certain system parameters and features with defined mechanical scenarios. The feature being most important for a vibration isolation system is the isolation, thus the transfer function between floor vibration and mass vibration.
But also, impacts of sound waves on material are known (Casimir effect, see “An acoustic Casimir effect”, Andres Larraza and Bruce Denardo, Phys. Lett. A 348, 151-155 !998)), which are of importance for vibration isolation systems.
These impacts are not or not sufficiently taken into consideration in case of known vibration isolation systems and of methods for designing vibration isolation systems respectively.